In a gas turbine engine, either axial or radial air entry swirlers are generally used in order to stabilize the flame in the combustor and promote mixing, more specifically at the primary zone region of the combustor. However, the swirl of the flow can decay along the combustor length due to various effect and phenomenon mostly related to the viscous forces and pressure recovery/redistribution. The wall friction also plays some part in reducing the swirl effect near the combustor wall region, by reducing the tangential component of the flow velocity.
The swirl decay thus causes quenching at the wall region, which usually increases unburnt hydrocarbons (UHC), leading to combustion inefficiency and high engine specific fuel consumption (SFC). A conventional way of reducing UHC includes increasing the temperature of the primary combustor section and defining effusion holes in the combustor wall, usually normal thereto, in selected area to push away and accelerate the flow attached to the wall region. However, the normal effusion flow in the primary zone generally creates a fresh supply of oxidant in an area of low flow velocity which, when combined with the high temperature of the combustor wall, usually limits the life of the combustor.
Also, the reduction in the tangential component of the flow velocity also usually leads to an increase in the axial component of the flow velocity, hence to a reduction in mixing between the hot combustion products and the dilution air entering the compressor, and to a reduction of the residence time of the flow in the hot path leading to the compressor turbine (CT) vanes. In addition, the loss of swirl reduces the angle of attack of the hot combustion gases exiting the combustor on the CT vanes, which usually reduces the life and performance thereof.
In order to correct the usual loss of swirl along the combustor, a longer duct or larger CT vanes can be used to improve mixing between the hot combustion products and the dilution air and increase the angle of attack of the hot combustion gases on the CT vanes. The geometrical angle of the compressor's diffuser pipe can also be increased, but due to the physical restriction of how much the diffuser pipes can be turned, such an angle increase usually necessitate the diffuser carrier disc to be larger. These solutions thus generally increase engine size, cost and weight.
Accordingly, improvements are desirable.